I have an API Gateway where I\'m setting the authentication to use AWS_IAM. This requires that I sign each request with the AWS V4 signature and attach the HMAC in the head
you can read on how the signature is done and you can (if you want). I would recommend pulling in the AWS SDK for .NET and using the functionality from the SDK to actually perform the signature.
Here is the signer form the SDK:
https://github.com/aws/aws-sdk-net/blob/6c3be79bdafd5bfff1ab0bf5fec17abc66c7b516/sdk/src/Core/Amazon.Runtime/Internal/Auth/AWS4Signer.cs
You may need to adapt it (ie it knows about AWS services and endpoints by default)